There are many different kinds of glue, so you can experiment with different solvents, but try paint remover. You can also scrape glue off, at the risk of damaging the wood. Solvents are safer (but don't smoke while you are working!).
ANS 2 - Solvents are NOT safer unless you have a painters filter mask on ! If this involves a lot of hard glue and you plan to put other floor covering down, then it's best to rent an industrial electric sander and sand it all off. Still wear a mask while doing this.
you have to put more glue on it, it will glue itself to the old glue, and be easier to remove
You should scrape the old glue off if you expect a flat surface.
Yes, it does . Old tile glue will ball up and mess your job.
I use a hair dryer to loosen glue and the clean with thinnersUse cigarette lighter fluid to clean off the old glue it works and it will not take off your paint.WD40 works wonders too.
There is no metal that starts off as glue.
The methods available depend on what the marks are or were caused by - which is not stated in the question.
To remove old tile glue from concrete floors, you can use a heat gun and a scraper to soften and scrape off the adhesive. Another option is to use a chemical adhesive remover specifically designed for this purpose. Be sure to wear proper protective gear and ventilate the area when working with chemicals.
Depends on the kind of glue - "Name your glue"
A girlfriend and/or wifeANS 2 - Whitlam's Glue Wash Hand Cleaner may work on that if it isn't too old. It works on clothing where ABS glue is 2-3 days old. -Available in many plumbing suppliers.
Depends what kind of glue.
Try Goof Off, it softens Super glue so you can pick it off.
It is a version of PVC glue.